This invention relates to the surface treatment of a windshield formed from a resin for use on a small and light vehicle such as a two- or three-wheeled motor vehicle, particularly one provided with a wiper.
If a windshield 1, as shown in FIG. 1 defining the fairing of a two-wheeled motor vehicle or the like is formed from a synthetic resin, it is low in surface hardness. Consequently, repeated wiper action is likely to damage the surface by scratching, abrasion or the like.
In order to avoid such damage, it is possible to fit in the center of the synthetic resin plate a glass plate insert which is sufficiently large to cover the area within which the wiper functions. This, however, leads to complications in the windshield manufacture and construction, an increase in the cost of the windshield, and a greater vehicle weight.
Coating the surfaces of a synthetic resin base with a hard resin is a generally known hardening coating treatment. This treatment makes it possible to reduce the complications of the windshield manufacture and construction, and any significant increase in the weight of the vehicle.
The prior art method of manufacturing a hard coated windshield comprises applying a uniform coating 4 to the surfaces of a flat resin base 3 to form a hard coated plate 2 as shown in FIGS. 2 and 3. Next as shown in FIG. 4, the plate is pressure formed and trimmed (FIG. 5) to eliminate the unnecessary portion 6 from an intermediate product 5. A finished windshield 1 as shown in FIG. 6 is obtained.
The coating 4 on the unnecessary portion 6 is, however, wasted. Also, since the hard coated resin base is naturally high in surface hardness, the press forming operation is likely to cause cracking of the coating 4, depending on the degree to which it is pressed.
When a two-wheeled motor vehicle is running, its vibration imparts a relatively high flexural load to the mounting portion 11 of a windshield 10 as shown in FIG. 7. Accordingly, it is preferable to form a thin coating on the mounting portion 11 so that it may not crack, while a thick coating is provided on that portion of the windshield against which the wiper rubs.
The method of manufacturing a windshield by press forming a hard coated plate, however, makes it relatively difficult to apply a locally varying coating thickness, or apply a coating to only a selected area.